Method for determining the active parathyroid hormone content in a sample, wherein the component of parathyroid hormone polypeptide chains which are oxidized at one or more sites near the PTH receptor binding structure having the amino acids 15 to 22 are specifically excluded from the content determination. Oxidation of the parathyroid hormone occurs in particular in dialysis patients, their blood plasma being exposed to an oxidation stress in the dialysis. The invention is based on the use of antibodies which bind specific conformation epitopes of the oxidised or reduced parathyroid hormone and its fragments. Further, there is provided a test system for the quantitative determination of parathyroid hormone and active fragments hereof in a sample.